Benjamin Dieltjens is mainly active as a chamber music player (on historical instruments as well as in the classical and new repertoire) and is regularly invited as such at many international festivals. In 1998 he was one of the founding members of the contemporary music group Het Collectief and he performs regularly with Ictus. He was a member of the former Ensemble für Neue Musik Karlsruhe directed by Peter Eötvös. He also forms a duo with his brother Thomas Dieltjens (piano).
He regularly plays with chamber groups such as Oxalys, Il Gardellino and Ensemble Explorations. Since 2007, Benjamin Dieltjens has been principal clarinet at deFilharmonie and he is a member of the Orchestre des Champs Elysées.
In 2008 he was invited as a principal clarinetist at the Royal Concertgebouw Orchestra Amsterdam. He was invited to coach The YM World Orchestra and gives seminars in contemporary chamber music and lectures on music after 1950 or the clarinet in new music for the Orpheus Institute and Matrix.